1. Field of the Invention:
The invention lies in the mechanical arts dealing with high-speed and timed product transfer and processing, and it is particularly suited to application in the printing field. Specifically, the invention relates to product transfer and product handling in high-speed folders, to timed signature transfer applications, and to web handling systems in printing presses.
2. Description of the Related Art:
Printing product must be transported in printing presses with accurate timing and proper speed. For instance, grippers are utilized to positively grip and feed single sheets into a sheet-fed printing unit. Timed grippers may also be used at the transfer points between individual printing units and at the delivery end for handling the individual signatures at the folder and/or at the stacker. Gripper systems are also used in web-fed rotary printing presses, for instance during make-ready to feed the web into the machine.
Various transfer devices, such as deliveries, carry the grippers on chains. The grippers are thereby disposed on gripper carriages of endlessly revolving chains. The grippers are typically timed and actuated in that a cam roller runs onto a gripper opening cam as the chain revolves around its track. These systems are similarly timed in the folders following the printing units in the product transport direction. The printed signature must thereby be folded at the speed of the upstream printing units and it is paramount that the signature be gripped and transported through the folder in a properly timed and controlled manner.
The chains in such gripper chain mechanisms tend to have a speed limiting effect and they require a high degree of maintenance. The chains typically require lubrication to ensure smooth and quiet operation.
It has been proposed to replace the chains in gripper transport systems with belts, typically urethane timing belts with weld-on profile. While the urethane belts provide several advantages over the chain systems, such belts are also limited with regard to their useable speed. The weld joint between the timing belt and the profile is substantially limited to a low tensile strength.
In the ever increasing speed of printing presses and related product handling apparatus, the speed of the gripper systems is a parameter of substantial importance. Also, proper tensile strength of the belts used in the systems is very important since any belt breakage can lead to a temporary shutdown of the printing press.